Hypocalcemia pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Vamsikrishna Gunnam M.B.B.S [2]
Overview
Hypocalcemia may develop in disorders associated with insufficient parathyroid hormone or vitamin D production or resistance to hormonal activities. Perturbations of calcium homeostasis can be caused by environmental factors or occur as a result of genetic mutations in the calcium-sensing receptor (as in type 1 autosomal dominant hypocalcemia), Gs α subunit (as in type 1A and 1B pseudohypoparathyroidism), vitamin D hydroxylase (as in type 1 vitamin D-dependent rickets , and calcitriol receptor (as in type 2 vitamin D-dependent rickets).
Pathophysiology
Physiology
The normal physiology of Hypocalcemia can be understood as follows:[1][2]
- The normal concentrations of calcium in the body is maintained within the narrow range and that is required for the minimal activity of the many extra- and intracellular processes calcium regulates.
- Calcium transport within the blood is mainly bound to plasma proteins like albumin (45%), phosphate and citrate(15%) and ionized state(40%).
- Only the ionized form of calcium is active but most laboratories show report of total serum calcium concentrations.
- The normal concentration of calcium ranges between 8.5 and 10.5 mg/dL.
- The normal range of ionized calcium in the plasma is 4.65 to 5.25 mg/dL.
Pathogenesis
It is understood that Hypocalcemia is the result caused by the following
Hypoalbuminemia
- When there is a fluctuation in the protein concentrations especially the one protein which is albumin,total calcium levels in the blood may change.[3][4]
- Whereas the levels of ionized calcium(free form) remains mostly constant, because it is hormonally regulated.
- So that the total serum calcium levels may not accurately reflect the physiologically important ionized calcium concentration.
Hormone regulation
- Parathyroid hormone (PTH) and vitamin D play a important role in regulating serum calcium.[5]
- Calcium by itself controls to regulate its own serum levels via a calcium-sensing receptor (CaSR) in the parathyroid gland to inhibit parathyroid hormone (PTH) secretion and on a CaSR in the loop of Henle of the kidney to stimulate renal calcium excretion.[6][7][8][9]
- Whenever the body serum ionized calcium goes down even in small amounts PTH (parathyroid hormone) is secreted instantaneously.And this occurs in 3 ways[10]
- 1)PTH (parathyroid hormone) stimulation of calcium reabsorption in the distal tubule of the kidney results in decreased urinary calcium excretion by the kidney.
- 2)PTH (parathyroid hormone) increases renal production of 1,25-dihydroxyvitamin D which is also called as calcitriol which in turn increases the intestinal calcium absorption.
- 3)PTH (parathyroid hormone) increases bone resorption which in turn increases the serum calcium levels.[11]
- When PTH secretion is insufficient Hypokalemia may occur as the sequel, which is classically seen in hypoparathyroidism.
Alkalosis
In alkalosis, hydrogen ions dissociate from the negatively charged albumin, which allows for increased calcium binding and leads to a decreased concentration of free calcium.
For an increase in pH of 0.1 unit, there is an approximately 0.05 mmol/L (0.1 mEq/L) fall in the serum level of ionized calcium.
Respiratory Alkalosis
Reduced ionized calcium concentration and hypocapnia associated with hyperventilation may contribute to symptoms of vasoconstriction including lightheadedness, fainting, and parasthesia.
Globulin Binding
Calcium binding to globulin is relatively small (1.0 g of globulin binds 0.2–0.3 mg of calcium) and generally does not influence the total serum calcium concentration.[12]
References
- ↑ Fong J, Khan A (February 2012). "Hypocalcemia: updates in diagnosis and management for primary care". Can Fam Physician. 58 (2): 158–62. PMC 3279267. PMID 22439169.
- ↑ Carroll R, Matfin G (February 2010). "Endocrine and metabolic emergencies: hypocalcaemia". Ther Adv Endocrinol Metab. 1 (1): 29–33. doi:10.1177/2042018810366494. PMC 3474611. PMID 23148147.
- ↑ Fong J, Khan A (February 2012). "Hypocalcemia: updates in diagnosis and management for primary care". Can Fam Physician. 58 (2): 158–62. PMC 3279267. PMID 22439169.
- ↑ Carroll R, Matfin G (February 2010). "Endocrine and metabolic emergencies: hypocalcaemia". Ther Adv Endocrinol Metab. 1 (1): 29–33. doi:10.1177/2042018810366494. PMC 3474611. PMID 23148147.
- ↑ Riccardi D, Brown EM (March 2010). "Physiology and pathophysiology of the calcium-sensing receptor in the kidney". Am. J. Physiol. Renal Physiol. 298 (3): F485–99. doi:10.1152/ajprenal.00608.2009. PMC 2838589. PMID 19923405.
- ↑ Goodman WG (January 2004). "Calcium-sensing receptors". Semin. Nephrol. 24 (1): 17–24. PMID 14730506.
- ↑ Quarles LD (July 2003). "Extracellular calcium-sensing receptors in the parathyroid gland, kidney, and other tissues". Curr. Opin. Nephrol. Hypertens. 12 (4): 349–55. doi:10.1097/01.mnh.0000079682.89474.80. PMID 12815330.
- ↑ Toka HR, Pollak MR (September 2014). "The role of the calcium-sensing receptor in disorders of abnormal calcium handling and cardiovascular disease". Curr. Opin. Nephrol. Hypertens. 23 (5): 494–501. doi:10.1097/MNH.0000000000000042. PMID 24992569.
- ↑ Egbuna OI, Brown EM (March 2008). "Hypercalcaemic and hypocalcaemic conditions due to calcium-sensing receptor mutations". Best Pract Res Clin Rheumatol. 22 (1): 129–48. doi:10.1016/j.berh.2007.11.006. PMC 2364635. PMID 18328986.
- ↑ Blaine J, Chonchol M, Levi M (July 2015). "Renal control of calcium, phosphate, and magnesium homeostasis". Clin J Am Soc Nephrol. 10 (7): 1257–72. doi:10.2215/CJN.09750913. PMC 4491294. PMID 25287933.
- ↑ Poole, K; Reeve, J (2005). "Parathyroid hormone — a bone anabolic and catabolic agent". Current Opinion in Pharmacology. 5 (6): 612–617. doi:10.1016/j.coph.2005.07.004. ISSN 1471-4892.
- ↑ Taal, Maarten (2012). Brenner & Rector's the kidney. Philadelphia, PA: Elsevier/Saunders. ISBN 978-1416061939.